Culpeper County climate

Culpeper County Frost Dates and Growing Season

NOAA 1991-2020 normals for Boston 4 Se, 14 km from Culpeper County, elevation 590 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Boston 4 Se. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 21 and the first fall freeze around October 22, a growing season of about 184 days.

Median at 36°F
last May 3, first October 13
Median at 32°F
last April 21, first October 22
Median at 28°F
last April 5, first November 1

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 20May 14May 10May 6May 3Apr 30Apr 27Apr 23Apr 19
32°FMay 10May 3Apr 28Apr 23Apr 21Apr 18Apr 15Apr 10Apr 5
28°FApr 23Apr 16Apr 12Apr 8Apr 5Apr 3Mar 31Mar 28Mar 23
24°FApr 6Apr 3Mar 31Mar 28Mar 25Mar 21Mar 17Mar 14Mar 8
20°FMar 28Mar 23Mar 19Mar 16Mar 13Mar 8Mar 5Mar 1Feb 24
16°FMar 19Mar 14Mar 8Mar 5Mar 1Feb 26Feb 21Feb 14Feb 8

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 2Oct 5Oct 8Oct 10Oct 13Oct 15Oct 18Oct 22Oct 25
32°FOct 8Oct 13Oct 17Oct 20Oct 22Oct 25Oct 28Nov 1Nov 4
28°FOct 17Oct 23Oct 27Oct 30Nov 1Nov 4Nov 6Nov 10Nov 15
24°FOct 30Nov 2Nov 5Nov 9Nov 11Nov 15Nov 20Nov 25Dec 1
20°FNov 7Nov 13Nov 17Nov 21Nov 25Nov 29Dec 2Dec 8Dec 15
16°FNov 18Nov 25Nov 30Dec 4Dec 9Dec 15Dec 20Dec 26Jan 2

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F181175170166162158154149143
32°F205197192188184180175170162
28°F230222217212208204200194187
24°F258250243238233229224219211
20°F285276269263258254249243234
16°F312302296290283278272264254

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
4,837
Cooling degree days, base 65°F
936
Growing degree days, base 40°F
5,931
Growing degree days, base 45°F
4,621
Growing degree days, base 50°F
3,472
Growing degree days, base 55°F
2,474
Growing degree days, base 60°F
1,627

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January98608
February80608
March675145
April35515169
May14354381
June17189622
July1306770
August3257719
September59101493
October31612200
November606144
December870013

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 14 km from Culpeper County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00440860 (Boston 4 Se). Public domain.